Epidemiology of Alternaria blight of Aloe barbadensis caused by Alternaria alternata

Indian Aloe (Aloe barbadensis Mill.), an important medicinal plant suffers from leaf spot disease caused by Alternaria alternata (Fr.) Keissler. Correlation of disease with environmental factors revealed that high relative humidity coupled with temperature of 27–28°C is most favourable for the disease development. The pathogen could survive in infected leaves upto 8 months under natural conditions and 10 months in vitro conditions, thus forming an important source of disease perennation. Aloe vera leaves showed susceptibility to the disease at all the stages (1 to 10 week old) but maximum susceptibility was at 10 week old leaves. Seven to nine days old cultures of A. alternata showed maximum virulence. Very young and very old cultures were found less virulent. Studies on conidial germination of A. alternata revealed that 25°C temperature and 100 per cent RH were most favourable for germination.